System optimization using compressed reticulated foam structures

ABSTRACT

Heterogeneously dense (relative density) continuous one-piece insoluble reticulated foam material with a continuous relative density gradient and/or distinct and marked relative densities and methods of manufacture.

TECHNICAL FIELD

Embodiments of the present invention relate to the technical field ofreticulated foam structures. More particularly, the embodiments of thepresent invention are directed toward heterogeneous reticulated foamstructures.

BACKGROUND OF THE INVENTION

DUOCEL® foam is a material manufactured by ERG Aerospace Corporation(www.ergaerospace.com). The material has been manufactured, engineeredto meet end user applications, and sold by ERG Aerospace Corporationsince 1967. The original manufacturing patent for DUOCEL® is listed asU.S. Pat. No. 3,616,841 and advances in manufacturing methods haveprogressed the use of DUOCEL® as a material solution for a broad numberof applications.

DUOCEL® is an open celled foam structure that takes on thecharacteristics of a base organic alloy. These base alloys typicallyconsist of low temperature alloys such as aluminum, copper, zinc, andother refractory metals. The advantages of an open celled foam structureis that the material offers high surface areas and outstanding strengthto weight ratios. Unlike closed cell foams, gases, liquids, and othermediums may pass through the pores of the material. This enables thematerial to be used in applications such as heat exchangers, energyabsorbers, baffles, structural support members, and other applicationsthat take advantage of the homogeneous open celled framework of thematerial.

DUOCEL® is manufactured in a range of pore sizes. These sizes include 5pores per inch (PPI), 10 PPI, 30 PPI, and 40 PPI. The advantage ofhaving different pore sizes is that the material may be optimized fordifferent applications. As an example, if high pressure gas diffusion isa primary requirement of an end user, then the 40 PPI material can bechosen to provide adequate pressure drop given the higher surface area.Conversely, a 5 PPI material may provide less pressure drop but thematerial may weigh less. Therefore, there is a weight and performanceconsideration for the specific PPI chosen. Specific examples of wherethis applies is with the design of filtration systems where flow ratesand pressure drops are primary input parameters for optimizing theperformance of a pump. Other applications include heat exchangers,energy absorbers, and other mechanical systems where there may exist aunique and single optimized system solution.

It is also possible to control the relative density of DUOCEL® for eachof the pore sizes referred to above. In other words, it is possible toadd material to the individual ligaments of DUOCEL® to create relativedensity ranges. As an example, a 5 PPI piece of DUOCEL® may be modifiedat the individual ligament level to achieve relative density rangesanywhere from 3 to 20 percent relative density (relative to the weightof the solid alloy). The relative density, much like the PPI, may bemodified as a design parameter to meet end user requirements. A DUOCEL®part or insert that maintains the same porosity and relative density isconsidered homogeneous.

Another unique feature of DUOCEL® is that the material is composed ofinterconnected solid ligament structures or cells. Conversely, opencelled foam materials that are manufactured using a chemical vapordeposition (CVD) type processes utilize a host structure as a base foradditive materials. These host structures are typically plastic or othermaterials that do not mirror the same composition as the CVD additive.The result is that CVD type manufactured foams are considered hollow andresult in lower yield stresses (or lower foam modulus). In other words,the individual ligaments lack a homogeneous make up and fail whenloading the material at lower thresholds then DUOCEL®. This materialdisadvantage reduces the yield stress of parts manufactured utilizingthe CVD technique, reduces thermodynamic properties of the material,creates non-homogeneous boundary layers between the CVD layers, andlimits the design power of using CVD parts for unique engineeringsolutions when compared to DUOCEL®.

Other additive manufacturing processes, to include 3-D printing, arealso at a disadvantage when compared to the versatility of DUOCEL®. Asmentioned above, inconsistent temperature profiles during the additivemanufacturing process create degraded boundary layer affects whencompared to DUOCEL®. Most 3-D printing techniques also create slipplanes in between layers. These factors cause additive manufacturingprocesses to be weaker (have a lower yield stress) and limits theirenergy absorption capabilities and pressure drop design capability.

One advantage that 3-D printing has over DUOCEL® is that the porosityand relative density of a supporting matrix may be varied across theentire part, validated, and then printed during the build process.Currently, 3-D printers are unable to print the complex geometries thatDUOCEL® provides.

In addition, open celled foam structures that are manufactured usingadditive processes, to include CVD and 3-D printing, often fail whencompressed due to the lower yield stress (foam modulus) and aretherefore limited to being densified to ranges below 30% relativedensity. The limit in the ability to compress these types of materialsreduces their ability to meet unique design solutions.

BRIEF SUMMARY OF THE INVENTION

Therefore, there is a need to create heterogeneous relative density opencelled DUOCEL® structures or inserts from an original homogeneousrelative density part in order to provide optimized system performanceDoing so would enable DUOCEL® the ability to directly compete with 3-Dprinted structures where relative density and porosity may be modifiedacross an entire part.

Furthermore, there is a need to create customized DUOCEL® parts whererelative density ranges anywhere from 3-85% for a single part in orderto provide engineers with versatile system solutions. These relativedensity ranges may be created by densifying the material along a singledirection (along the x-axis), across two directions (along the x-yaxes), or across the material in three dimensions (along the x-y-zaxes).

It is a further objective of the present invention to createheterogeneous DUOCEL® structures where the relative density rangediffers throughout the structure when densified. These types ofstructures offer a versatile material solution where each zone ofDUOCEL® is densified to meet any number of system requirements within azone or presents a progressive range of relative densities across thestructure.

It is yet a further objective of the present invention to introducemethods of manufacturing that creates heterogeneous foam structures anddensified foam structures utilizing presses and dies. These types ofmanufacturing procedures are inexpensive and tight tolerances can beheld. Reduced setup time for the dies and presses, the simplicity of ahydraulic press when compared to tooling machines, and overallthroughput makes this approach inexpensive and more efficient whencompared to CNC machinery or 3-D printing.

It is a further objective of the present invention to use heterogeneousDUOCEL® parts or inserts as energy absorbers, filters, heat exchangersor other applications where system performance may be optimized throughheterogeneous relative densification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a perspective view of a homogeneous relative densitycontinuous one-piece insoluble reticulated open celled foam material(1).

FIG. 2 is a perspective view of a single cell (2) of a homogeneousrelative density continuous one-piece insoluble reticulated open celledfoam material (1).

FIG. 3 is a perspective view of a heterogeneous relative densitycontinuous one-piece insoluble reticulated open celled foam material(5).

FIG. 4 is a perspective view of a single cell (2) of a heterogeneousrelative density continuous one-piece insoluble reticulated open celledfoam material (5) after densification.

FIG. 5A is a table that provides data points from stress-strainrelationships from densification of a heterogeneous relative densitycontinuous one-piece insoluble reticulated open celled foam material(5).

FIG. 5B is a stress strain curve that demonstrates the differentrelative density properties of a single heterogeneous relative densitycontinuous one-piece insoluble reticulated open celled foam material (5)when assessed for different sections of the material (L1-L3).

FIG. 6A is a perspective view of an application where a singleheterogeneous relative density continuous one-piece insolublereticulated open celled foam material (5) is used to demonstrate energyabsorption system optimization.

FIG. 6B is a perspective view of the same system above.

FIG. 7 is a perspective view of an example of a die set formanufacturing heterogeneous relative density continuous one-pieceinsoluble reticulated open celled foam material.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention will now be described in detail with reference tothe accompanying drawings, wherein the same reference numerals will beused to identify the same or similar elements throughout the severalviews. It should be noted that the drawings should be viewed in thedirection of orientation of the reference numerals.

FIG. 1 illustrates a homogeneous relative density continuous one-pieceinsoluble reticulated open celled foam material (1). The part has arelative density of 10%.

FIG. 2 illustrates a single cell (2) of a homogeneous continuesone-piece insoluble reticulated open celled foam material (1) where eachcell (2) is generally characterized as a bubble shaped 14 sidedpolyhedral or solid shape tetrakaidekahedron. Within each cell (2) is aseries of pores (3) that create the open celled architecture and eachpore (3) is defined by a number of solid ligaments (4). These ligaments(4) take on the properties of the base alloy and examples includealuminum, titanium, copper, and other metals. Typically, the ligamentwidth is 0.025 mm to 0.65 mm, such as 0.028 mm to 2.8 mm, 0.05 mm to 2.8mm, 0.05 mm to 0.5 mm, 0.05 to 0.65 mm, 0.1 mm to 0.5 mm, 0.1 mm to 0.7mm, or any range of values falling between 0.025 mm and 0.7 mm. Forexample, a 10 PPI material can have a mean value ligament thickness of0.41 mm or a 20 PPI material can have a mean value ligament thickness of0.31 mm, while a 40 PPI material can have a mean value ligamentthickness of 0.18 mm.

Ligament (4) thickness differs based on the density of the homogeneouscontinuous one-piece insoluble reticulated open celled foam material(1). As shown in FIG. 2, a 10% relative dense ligament that consists of10 pores (3) per inch (approximated) has a mean value thickness diameteror width of approximately 0.041 mm. This creates an average cell (2)diameter for the material shown to be approximately 2.2 mm.

FIG. 3 illustrates a single heterogeneously dense (relative density)continuous one-piece insoluble reticulated foam material (5) that hasbeen fabricated from a homogeneous relative density continuous one-pieceinsoluble reticulated open celled foam material (1). The part has anoverall width w, height h, and length L and, in this example, thedensity varies along the length L of the part. In fact, average relativedensities vary across and along three different sections of the part.Section one (6) of the part remains at 10 pores (3) per inch, 10%relative density, and remains unchanged along the length L1. Section two(7) of the part remains at 10 pores (3) per inch but the relativedensity over the length L2 has increased to an average of 25% where cellsize diameter is approximately 1.2 mm. Likewise, section three (8) hasincreased relative density to an average of 35% along length L3 and acell size diameter of approximately 0.8 mm.

Typically, average cell diameters in heterologous relative densitycontinuous one-piece insoluble reticulated foam material (5) range fromabout 0.35 mm to about 4 mm, such as 0.8 mm to 0.38 mm. If thedensification process is continuously gradual across the heterologousrelative density continuous one-piece insoluble reticulated foammaterial (5), then all intervening fractions between the relativedensity of the least dense portion and the relative density of the mostdense portion are represented. If, however, a part made from theparticular heterologous relative density continuous one-piece insolublereticulated foam material (5) is desired to have a number of setrelative densities that occur within the part in some type of astep-wise manner, then the average cell diameters associated with onlythose relative densities will be present. For example, if the partrequires a portion with a relative density of 10%, that is adjacent to aportion with a relative density of 33%, that is adjacent to a portionwith a relative density of 25%, then the average cell size diameterspresent in the part will be about 2.8 mm (10% relative density), 0.8 mm(33% relative density), and 1.2 mm (25% relative density).

FIG. 4 illustrates the changes of the ligament (4) after densificationreaching the 35% relative density of section three (8). While theligament (4) is shown to have buckled, the overall structural integrityof the deformed pores (16) remains intact and therefore providesstrength to the heterogeneously dense (relative density) continuousone-piece insoluble reticulated foam material (5). Likewise, thecollapsing of the cell (2) volume provides increased fluid impedancewhen compared to the original relative density. The changes madetherefore afford one to modify the stress strain performancecharacteristics and the impedance ability of the foam to enhance systemoptimization.

Laboratory experimentation has confirmed stress-strain relationships ofthe single heterogeneously dense (relative density) continuous one-pieceinsoluble reticulated foam material (5) for each of the sections (6-8)illustrated as a demonstration. More specifically, experimentation wasconducted and load vs. deflection readings were obtained in thefollowing manner: During the first 100 mils of deflection, readings weretaken at intervals of 10 mils; thereafter, readings were recorded every50 mils until either a deflection of 500 mils was reached, or 150 milswith a load in excess of 1000 pounds was reached, or 150 mils with aload in excess of 10000 pounds was reached, or 10000 pounds was reachedafter 150 mils, but before 500 mils. Data points collected are presentedin FIG. 5A.

FIG. 5B shows the stress-strain curves associated with each section(6-8) of the single heterogeneously dense (relative density) continuousone-piece insoluble reticulated foam material (5). This loadingdistribution across the entire length L of the single heterogeneouslydense (relative density) continuous one-piece insoluble reticulated foammaterial (5) is done to demonstrate how a single part can meet versatiledesign requirements where complex and different energy absorbingproperties throughout the length L might be required.

One example of the value of a single heterogeneously dense (relativedensity) continuous one-piece insoluble reticulated foam material (5) isthe design and fabrication of a blunt trauma foam protection barrier(11) as shown in FIG. 6. While body armor (10) provides protection forsoldiers and first responders against bullets, the protective platecharacteristically used in such devices cannot alone reduce backsidespalling that occurs when a bullet strikes the protective plate. Inother words, people who are shot when wearing body armor typicallyexperience blunt trauma due to the backside effects of the protectiveplate.

Utilizing a single heterogeneously dense (relative density) continuousone-piece insoluble reticulated foam material (5) within a body armor(10) system, one may reduce the energy translated from the body armor(10) to the individual. Furthermore, by changing the relative density ofthat additional foam protection barrier (11), vital organs (such as theheart that which is centered near the middle of the chest) are protectedwith a thicker foam protection barrier (11) where needed most. Likewise,the thinner foam located at the edges of the protection barrier (11)within the body armor (10) provides ample protection but also allows theindividual to be unencumbered in movement due to the low volume of thedevice.

FIG. 7 illustrates an example of a die set (12) that manufactures thefoam protective barrier (11) mentioned above. The die set (12) consistsof a male press (13), a female press (14), and a place to insert ahomogeneous (relative density) continuous one-piece insolublereticulated open celled foam material (1) in order to transform it intoa single heterogeneously dense (relative density) continuous one-pieceinsoluble reticulated foam material (5). To accomplish this, a series ofmanufacturing steps must be implemented.

First, the homogeneous relative density continuous one-piece insolublereticulated open celled foam material (1) must be structurally weakenedthrough a heating process if the parts measure thicker than 6 mmTypically, homogeneous relative density continuous one-piece insolublereticulated open celled foam material (1) that is equal to or greaterthan 6 mm thick is heated to 20-200° C. Heating and weakening thestructure may not be needed for parts less than 6 mm thick because smallparts tend to have few cells (2) and thereby have adequate space todensify without interference. In other words, a thin 10 pores (4) perinch part with an original 10% relative density is limited in itsability to reach high relative densities simply because the lack ofmaterial present prevents it. As an example, a thin part might only beable to reach a maximum density of only 20 to 25% relative density.

For larger parts, a heating process, heat treatment, or annealingprocess is undertaken to change the material properties of the hostalloy, as mentioned above. Ideally, this process softens the materialand enables it to become less brittle and more ductile thereby ensuringuniform ligament (4) buckling during densification. After thedensification process, strength is returned to the product by subjectingthe heterogeneously densified (relative density) foam material (5) to aheat treatment according to ASTM International standards appropriate forthe metal or alloy used in the homogeneous relative density continuousone-piece insoluble reticulated open celled foam material (1).

Once the material has been modified, the press and die procedure maybegin. This is initiated by first placing the homogeneous relativedensity continuous one-piece insoluble reticulated open celled foammaterial (1) within a female die set. Once in position, a male die setis placed on top of the part and pressing is slowly initiated. This rateis typically no faster than 100 mils/second. The amount of pressure willvary depending upon the thickness of the homogeneous relative densitycontinuous one-piece insoluble reticulated open celled foam material (1)used and/or the PPI of that material. Pressures range from 1,000 psi to40,000 psi, such as 5,000 psi to 20,000 psi, but can include any rangeof pressures falling within 1,000-40,000 psi.

It should also be noted that this process must be done in stages whenachieving higher relative density levels is desired. More specifically,when parts are pressed and the densities approach 20% relative density,the parts are removed, cleaned, and then loaded into secondary pressesand dies which further densify the material as needed. This treatmentwith secondary presses addresses the spring-back memory action of thematerial and provides a more uniform overall compression.

In addition to a stepped press approach, it should also be noted thatthe material may only be compressed up to levels of 70% relative densitywhen heating in the 20-200° C. range. Further densification is possible,but temperatures within the part must be nearing the molten state of thebase alloy to reach relative densification levels of more than 70%, suchas 72.5%, 75%, 77.5%, 80%, 82.5%, 85%, 87.5% or more.

1.-19. (canceled)
 20. A heterogeneously dense continuous one-pieceinsoluble reticulated open-celled foam metal or alloy materialcomprising (a) partially collapsed open cells ranging in size and havinga maximum diameter of 4 mm and a minimum diameter of 0.35 mm; (b)ligaments having a width of 0.025 mm to 0.7 mm; (c) pores formed by theligaments; and (d) a relative density gradient within theheterogeneously dense one-piece insoluble reticulated open celled foammetal or alloy material ranging from at least 3% in density at a leastdense point to 85% density at a most dense point.
 21. Theheterogeneously dense foam material of claim 20, wherein the relativedensity gradient is continuous across the one-piece insolublereticulated open-celled foam metal or alloy material.
 22. Theheterogeneously dense foam material of claim 20, wherein the relativedensity gradient is formed from the collapsing of the cells.
 23. Theheterogeneously dense foam material of claim 20, wherein pores formed bythe ligaments are deformed.
 24. The heterogeneously dense foam materialof claim 20, wherein the relative density gradient occurs along a singledirection.
 25. The heterogeneously dense foam material of claim 20,wherein the relative density gradient occurs across two directions. 26.The heterogeneously dense foam material of claim 20, wherein therelative density gradient occurs across three dimensions.
 27. Theheterogeneously dense foam material of claim 20, wherein the relativedensity within the foam material is a continuous gradient that rangesfrom 10% to 33% and all values therebetween.
 28. The heterogeneouslydense foam material of claim 20, wherein the relative density within thefoam material is a continuous gradient that ranges from 25% and 70%, andall values therebetween.
 29. The heterogeneously dense foam material ofclaim 20, wherein the relative density gradient within the foam hasdistinct and marked differences.
 30. The heterogeneously dense foammaterial of claim 29, wherein the relative density within the foam is10%, 25%, and 33%.
 31. The heterogeneously dense foam material of claim29, wherein the relative density within the foam is 25% and 33%.
 32. Theheterogeneously dense foam material of claim 20, wherein the celldiameters have a maximum diameter of 3.72 mm and a minimum diameter of0.55 mm.
 33. The heterogeneously dense foam material of claim 20,wherein the ligament width is 0.028 mm to 0.65 mm.
 34. Theheterogeneously dense foam material of claim 20, wherein the pore sizeis 0.025 mm to 0.65 mm.
 35. A blunt trauma foam protection barriercomprising the heterogeneously dense foam material of claim
 20. 36. Aheat exchanger comprising the heterogeneously dense foam material ofclaim
 20. 37. An energy absorber comprising the heterogeneously densefoam material of claim
 1. 38. A filter comprising the heterogeneouslydense foam material of claim 1.